1. Field of the Invention
This invention relates to a secondary arc extinction device in an electric power system in accordance with which a secondary arc is actively extinguished so as to shorten substantially a reclosing nonvoltage period of time.
2. Description of the Prior Art
In general, there is employed a multiphase, multiconductor transmission line having a large electrostatic coupling capacity between phases and between high voltage lines of large current capacity. In case a short-circuit is caused in a transmission line by a damage caused by lightning or the like, however, an induced electric current is supplied from other whole phases or whole lines via the above-mentioned electrostatic coupling despite the fact that the line is protected by circuit breakers at both the ends thereof. As the result, an arc generated by back flashover (which is hereinafter referred to as a "secondary arc") is not extinguished. Thus, when the single/multiphase reclosing is effected, it is required to have a suficient reclosing nonvoltage period of time, which is not desired from the standpoint of the stability of the system.
Hereinafter, an explanation is given concerning this. If there is caused a short-circuit in a transmission line in an electric power system, an arc current continues to flow for a time despite the fact that the circuit breakers at both the ends thereof terminate the line. Thus, the problem condition is not removed. This is due to the fact that the secondary arc continues as shown in FIG. 1 by an electrostatic induction by the whole phase or the whole line. This tendency is more outstanding in a high voltage transmission line of large current capacity wherein the electrostatic coupling capacity between lines is large.
In view of the above, it is under consideration to provide a reactor to cancel the electrostatic capacity between lines in a high voltage transmission line of large current capacity so as to extinguish the secondary arc. The arrangement of this extinguishing reactor is as shown in FIG. 2 and FIG. 3. The extinguishing reactor is provided at the side of the line of an electric station or a substation.
The extinguishing function by the reactor which is shown in FIG. 2 is explained as follows. The matrix of the transmission line admittance Y.sub.C is expressed by the formula (1), while the matrix of the extinguishing reaction admittance Y.sub.L is expressed by the formula (2). ##EQU1##
The total admittance Y is as axpressed in the formula (3): EQU Y=Y.sub.C +Y.sub.L ( 3)
Since the characteristics of Y.sub.L and Y.sub.C are different from each other, it becomes possible to make zero the mutual admittance as in the formula (4) by suitably choosing the value of Y.sub.L. In other words, it becomes possible to make zero the coupling between the lines. As the consequence, it becomes pessible to extinguish the secondary arc. ##EQU2##
However, it is impossible to make zero the electrostatic induction from a whole line in the case of juxtaposed transmission lines with the above-mentioned arrangement of an extinguishing reactor. (Reference formula (5) as well as formula (6)). It is very difficult to distinguish the secondary arc. ##EQU3##
Then, in order to remove the above-mentioned draw-backs, it has recently been considered to arrange an extinguishing reactor in such a way as shown in FIG. 3.
The extinction function in accordance with the reactor which is shown in FIG. 3 is nextly explained. The admittance matrix of the extinguishing reactor which is shown in FIG. 3 is expressed by the formula (7). If Y.sub.L is chosen in the formula (7) in such a way that the admittance of the transmission line in the formula (5) is cancelled, it becomes possible to make zero the electrostatic induction from the adjacent line, thereby making it possible to extinguish the secondary arc. ##EQU4##
On the other hand, there has conventionally been considered a system in accordance with which the value of Y.sub.L in the above-mentioned reactor system is set constant or at a certain calculated value by identifying the troubled phase. However, the value of Y.sub.L then does not necessarily become the most suitable value and it becomes impossible to extinguish the secondary arc within a short period of time because the admittance of the transmission line varies due to the troubled phase and, in addition, considerable errors are contained in calculating the line constant which also becomes the reference in setting the most suitable Y.sub.L by calculation.